1. Field of the Invention
The present invention relates to a multilayer wiring board, a semiconductor device mounting board using such a wiring board, and a method of manufacturing such a multilayer wiring board.
2. Description of the Background Art
In recent years, the trend towards increased miniaturization and functionality of electronic equipment has produced a growing demand for higher density mounting of electronic components on the mounting boards used for mounting such electronic equipment. In order to enable these electronic components to be mounted on the mounting boards with higher densities, there are calls not only for further miniaturization of the electronic components, but also for finer and higher precision wiring processing on the printed wiring boards.
On the other hand, in order to ensure a minimal environmental impact, these days it is also necessary to consider the recycling of the aforementioned mounting boards. Consequently, wiring boards comprising a thermoplastic resin as a primary material have been attracting considerable attention.
These wiring boards use a highly heat resistant thermoplastic resin known as super engineering plastic, and not only enable finely detailed, high precision wiring processing, but also offer a number of other advantages including a high degree of mechanical strength, superior electrical insulation, and comparative ease of recycling. As a result, in order to meet the demands for increased wiring density, considerable research is being conducted into the use of highly heat resistant thermoplastic resins as the substrate materials for printed wiring boards.
Examples of thermoplastic resins which are used as these substrate materials include liquid crystal polymers and thermoplastic polyimides.
Furthermore, in a printed wiring board using one of these thermoplastic resins, a predetermined wiring circuit is formed on top of the printed wiring board in a similar manner to a conventional general purpose printed wiring board, namely using a so-called wet process in which copper foil is laminated on top of the printed wiring board, and the copper foil is then subjected to etching treatment using wet etching or the like to form the wiring pattern.
Other methods of forming the wiring circuit on the printed wiring board include methods in which the wiring circuit is formed by a dry process.
In these methods, screen printing techniques or dispensing techniques are used to print a conductive paste onto the printed wiring board in a predetermined wiring pattern, and this conductive paste is then subjected to heat treatment to complete the formation of a predetermined wiring circuit on the printed wiring board.
This method of printing on a conductive paste does not require the wet etching process used in conventional copper foil etching methods, and consequently the manufacturing process can be converted to a dry process, which offers the advantage of being even gentler on the environment.
The thermoplastic resin enables a shortening of the process tact, and also offers the advantages of superior moldability and plasticity, and is consequently considered a very favorable material as a board substrate material.
However, although conventional highly heat resistant thermoplastic resins offer advantages as highly heat resistant substrate materials, when the thermoplastic resin is laminated and integrated into a single unit, the resin must be heated to a temperature close to the resin melting point to ensure thermal fusion, and a problem arises during this heating and thermal fusion in that a resin flow, resulting from the large reduction in the modulus of elasticity at temperatures near the melting point, may cause distortions in the conducting material which forms the wiring circuit.
In addition, conventional printed wiring board production lines are suited to high volume low mix production, and consequently there is tendency for the production facilities to increase in size. Furthermore, chemical etching (wet etching) and plating techniques are typically used during the formation of wiring circuits on the printed wiring boards, and these techniques are undesirable from the viewpoint of environmental impact.
Furthermore as described above, examples of methods for wiring formation using dry processes include screen printing methods and dispensing methods using a conductive paste, although in both of these methods, there is a limit to the improvements in detail and precision of the conductive wiring which can be achieved in order to try and meet the ever increasing demands for higher density mounting.
In addition, as described above, in a laminated product of a thermoplastic resin on which a wiring circuit has been formed using a conductive paste, the resin must be heated to a temperature close to the melting point and subjected to pressure to fuse the thermoplastic resin layers together to create a single integrated unit, and as the pitch of the wiring becomes finer, distortion of the wiring resulting from resin flow during lamination is increasingly becoming a factor which cannot be ignored in substrate design.
The present invention aims to resolve the problems described above with an object of providing a multilayer wiring board with a high degree of heat resistance, which is capable of low temperature fusion without the occurrence of resin flow, enables high precision, finely detailed conductive wiring, can be ideally applied to low volume high mix manufacturing configurations, and also has little impact on the environment, as well as providing a semiconductor device mounting board using such a multilayer wiring board, and a method of manufacturing such a multilayer wiring board.
As a result of intensive research, the inventors of the present invention realized that if a substrate formed from a thermoplastic resin could be combined with a wiring pattern formed from a conductive paste to produce a wiring board, then a high performance, environmentally friendly multilayer wiring board could be produced, and were hence able to complete the present invention.
In other words, in a multilayer wiring board of the present invention, a wiring circuit is formed by embedding conductive wiring within an insulating substrate, formed from a thermoplastic resin composition comprising a polyarylketone resin with a crystalline melting peak temperature of at least 260xc2x0 C. and an amorphous polyetherimide resin as the primary constituents, so that the surface of the wiring protrudes to the surface of the resin, and a plurality of wiring substrates, formed by smoothing the surface of an insulating substrate comprising embedded conductive wiring are laminated together, and wiring is provided which electrically connects the wiring substrates (1, 2, 3, 4) to one another, and the insulating substrates of these wiring substrates are bonded together by thermal fusion and crystallized, and the conductive wiring of the wiring circuit of each wiring substrate and the wiring used for electrically connecting each of the wiring substrates together, is formed from a conductive material produced by curing a conductive paste.
In this type of multilayer wiring board, the insulating substrate which forms an essential component of the wiring substrate utilizes a thermoplastic resin composition comprising a polyarylketone resin with a crystalline melting peak temperature of at least 260xc2x0 C. and an amorphous polyetherimide resin as the primary constituents, and conductive wiring is embedded within the insulating substrate formed from this thermoplastic resin composition so that the surface of the wiring protrudes to the surface of the resin composition. By subsequently laminating a plurality of these wiring substrates and then bonding and crystallizing the wiring substrates through thermal fusion of the insulating substrates, a multilayer wiring board with excellent heat resistance, a high degree of mechanical strength and excellent electrical insulation can be achieved, and in addition, low temperature fusion is possible without the occurrence of resin flow, meaning the problem of wiring distortions resulting from such resin flow can be resolved, making high precision, finely detailed conductive wiring possible. As a result, a multilayer wiring board with excellent electrical characteristics and reliability can be provided.
Furthermore, by appropriate selection of both the thermoplastic resin composition, and the type and shape of the conductive wiring, a variety of different wiring substrates can be formed, and as a result, by combining wiring substrates with different specifications, the present invention can be applied to multilayer wiring boards with a wide variety of specifications.
In addition, the combination of a variety of wiring substrates of different specifications makes the invention ideally suited to low volume high mix type manufacturing configurations. Furthermore, by using a conductive paste for the electrical connections, wiring formation using wet processes becomes unnecessary, meaning the environmental impact can be reduced.
The aforementioned insulating substrate should preferably utilize an amorphous film produced by molten mixing and then rapid cooling of a thermoplastic resin composition comprising a polyarylketone resin with a crystalline melting peak temperature of at least 260xc2x0 C. and an amorphous polyetherimide resin as the primary constituents.
Furthermore, the conductive wiring of the present invention preferably comprises a conductive material formed by curing a conductive paste and a metallic foil, with at least the surface of the metallic foil protruding to the surface of the substrate.
A semiconductor device mounting board of the present invention comprises a multilayer wiring board of the present invention with a semiconductor device mounted thereon.
According to a semiconductor device mounting board of the present invention, because the semiconductor device is mounted on a multilayer wiring board of the present invention, a high precision, finely detailed and high density semiconductor device mounting board can be produced with relative ease.
A method of manufacturing a multilayer wiring board according to the present invention comprises the steps of performing thermal molding on either one surface or both surfaces of an insulating substrate formed from a thermoplastic resin composition comprising a polyarylketone resin with a crystalline melting peak temperature of at least 260xc2x0 C. and an amorphous polyetherimide resin as the primary constituents, at a temperature which is higher than the glass transition temperature of the thermoplastic resin composition but lower than the crystallization start temperature, thereby forming a conductive region comprising grooves, via holes, or a combination of grooves and via holes on the aforementioned one surface or both surfaces, subsequently filling the conductive region with a conductive paste and forming a wiring circuit in which the conductive paste functions as conductive wiring, thereby forming a wiring substrate comprising the insulating substrate and the wiring circuit, and subsequently laminating a plurality of these wiring substrates together, bonding and crystallizing the insulating substrates of these wiring substrates by thermal fusion at a temperature higher than the aforementioned crystallization start temperature, and electrically connecting the plurality of wiring substrates with conductive paste.
In this method of manufacturing a multilayer wiring board, a wiring substrate is generated by forming a wiring circuit comprising conductive wiring formed from a conductive paste on an insulating substrate formed from a thermoplastic resin composition comprising a polyarylketone resin with a crystalline melting peak temperature of at least 260xc2x0 C. and an amorphous polyetherimide resin as the primary constituents, and a plurality of these wiring substrates are then laminated together, and the insulating substrates of these wiring substrates are then bonded together and crystallized by thermal fusion at a temperature higher than the aforementioned crystallization start temperature, while each of the wiring substrates are electrically connected together with conductive paste. Consequently, a multilayer wiring board with excellent heat resistance, a high degree of mechanical strength, excellent electrical insulation, and with high precision and finely detailed conductive wiring can be produced with relative ease. As a result, a multilayer wiring board with excellent electrical characteristics and reliability can be produced with relative ease.
Furthermore, by appropriate selection of the number of insulating substrates and the wiring circuits formed thereon, a variety of different wiring substrates can be formed, and by combining these wiring substrates, multilayer wiring boards with a wide variety of specifications can be produced with relative ease, meaning low volume high mix multilayer wiring boards can be prepared easily, and within a relatively short time period. Furthermore, in the manufacturing process, by employing a dry process in which electrical connection is achieved via a conductive paste, wiring formation processes relying on wet processes become unnecessary, meaning the environmental impact of the manufacturing process is lessened considerably.
In this method of manufacturing a multilayer wiring board, the insulating substrate should preferably utilize an amorphous film produced by molten mixing and then rapid cooling of a thermoplastic resin composition comprising a polyarylketone resin with a crystalline melting peak temperature of at least 260xc2x0 C. and an amorphous polyetherimide resin as the primary constituents.
Another method of manufacturing a multilayer wiring board according to the present invention comprises the steps of positioning an impressing jig on one surface of an insulating substrate formed from a thermoplastic resin composition comprising a polyarylketone resin with a crystalline melting peak temperature of at least 260xc2x0 C. and an amorphous polyetherimide resin as the primary constituents, with a metallic foil disposed therebetween, and positioning an elastic film, which displays a lower modulus of elasticity than the insulating substrate at temperatures lower than the glass transition temperature of the insulating substrate, on the other surface of the insulating substrate, subsequently using the impressing jig for performing thermal molding at a temperature which is higher than the glass transition temperature of the elastic film but lower than the crystallization start temperature of the insulating substrate, and subsequently peeling off the metallic foil, so that only those sections of the metallic foil in positions corresponding with convex sections of the impressing jig are fused to the insulating substrate.
According to this method of manufacturing a multilayer wiring board, an impressing jig is positioned on one surface of the insulating substrate formed from a thermoplastic resin composition comprising a polyarylketone resin with a crystalline melting peak temperature of at least 260xc2x0 C. and an amorphous polyetherimide resin as the primary constituents, with a metallic foil disposed therebetween, and an elastic film, which displays a lower modulus of elasticity than the insulating substrate at temperatures lower than the glass transition temperature of the insulating substrate, is positioned on the other surface of the insulating substrate, and in this state, by carrying out thermal molding by pressing the impressing jig against the insulating substrate at a temperature which is higher than the glass transition temperature of the elastic film but lower than the crystallization start temperature of the insulating substrate, only those sections of the metallic foil in positions corresponding with convex sections of the impressing jig are fused firmly to the insulating substrate. Consequently, a multilayer wiring board with excellent heat resistance, a high degree of mechanical strength, excellent electrical insulation, and with high precision and finely detailed conductive wiring can be produced with relative ease. As a result, a multilayer wiring board with excellent electrical characteristics and reliability can be produced with relative ease.
Furthermore, by appropriate selection of the number of insulating substrates and the wiring circuits formed thereon, a variety of different insulating substrates and conductive wiring can be formed, and by combining these substrates and wiring, multilayer wiring boards with a wide variety of specifications can be produced with relative ease, meaning low volume high mix multilayer wiring boards can be prepared easily, and within a relatively short time period. Furthermore, in the manufacturing process, by employing a dry process in which electrical connection is achieved via a conductive paste, wiring formation processes relying on wet processes become unnecessary, meaning the environmental impact of the manufacturing process is lessened considerably.